Analytes, such as nucleic acids from a target organism, are typically part of a larger sample, with the rest of the material within the sample ranging from trace amounts to very abundant. These materials often interfere with or completely prevent detection of the organism and can make quantitative results impossible. Various extraction protocols and devices have been used to purify the sample, most of which are optimized for certain samples and applications, and usually require bench-top equipment used within a laboratory environment by highly skilled personal. Performing such extraction protocols in the field is difficult and often impossible due to logistical complexities associated with taking laboratory equipment out of the laboratory and into the field. A laboratory environment can also be controlled, whereas such control is limited out in the field.
Biological assays are particularly plagued with the added issue of the analyte's stability, viability, or even mutation, within the sample itself or sample purification methodology. Thus, for biological analysis, the challenges include two equally important and interacting factors: accuracy of the analytical method and efficiency of the sample purification for the analyte in the sample matrix. Since sample matrices are highly variable, a universal preparation protocol remains elusive.
The ability to process large volume liquid samples for PCR (polymerase chain reaction) based testing is ubiquitous to many different sample types. Water testing often demands analyses of sample volumes of tens to hundreds of milliliters to compensate for target dilution, with microbes, along with other particulates, typically concentrated into a smaller volume by a series of filtering and centrifugation steps. For air samples, particulates are captured either directly in collection fluid or on a filter and then eluted into a liquid. Soil samples involve suspending the soil in a liquid to release particulates from the soil colloids. Examples of large volume liquid samples include biological samples, such as blood for screening, or pharmaceutical samples for product validation. Samples are taken to a laboratory environment to perform analysis.